Adds zsh completion

Use nova bash-completion to add native zsh completion using built in
parameter expansion.  Nothing spectacular or new, this is mostly so that
zsh users do not need to autoload bashcompinit just to use nova.

Change-Id: I56f62f036e0c85e79197f4c7dfd25abf7eb4110a
Implements: zsh completion
Merge "Adds zsh completion"